Technical Blog Post
"Required" input mode not working for YORN attributes
Is it possible to make a YORN field required?
This cannot be done with a YORN type attribute.
The "required" input mode works when the field is null.
So you cannot save the record if the field is null, because a value is required.
However, the YORN field is never null. If the field is not checked, the value in the DB is "N". If checked is "Y".